1. Field of the Invention
The present invention relates to a through anchor which is applied to a seat belt device for a vehicle, and around which a webbing for restraining a vehicle occupant is trained, and which supports the webbing at a vehicle body, and to a method of manufacturing the through anchor.
2. Description of the Related Art
A three point seat belt device using a continuous webbing is known as a seat belt device for a vehicle.
In this type of seat belt device, one end portion of the webbing is anchored at a retractor, and the other end portion of the webbing passes through a through anchor and is anchored to an anchor plate. When a vehicle occupant applies the webbing to himself/herself, he/she engages a tongue plate, which is disposed at an intermediate portion of the webbing between the anchor plate and the through anchor, with a buckle device. The webbing is thereby pulled out from the retractor and set in a state of being applied to the vehicle occupant.
The through anchor, around which the webbing is trained and which is for supporting the webbing at the vehicle body as described above, is generally structured such that a resin material is integrally molded with a metal main body portion (a metal plate). In this way, the edge portions and the like of the metal main body portion are covered and are not exposed to the exterior. Moreover, in such a through anchor, in order for the webbing to be drawn-out and taken-up smoothly, a structure is known in which a resin piece, which is formed of a synthetic resin material such as polyacetal or high molecular weight polyethylene or the like, is fixed to the portion of the through anchor along which the webbing slides, so as to decrease the coefficient of friction with the webbing.
However, in a through anchor having the above-described structure, when a large load is applied to the webbing at the time when the vehicle rapidly decelerates, because the coefficient of friction of the resin piece is low, there are cases in which the webbing slips laterally within the insert-through hole and moves toward and gets stuck at one end of the insert-through hole, such that so-called jamming occurs.
Thus, the forming of plural grooves in the surface of the resin piece is know as a means for preventing jamming while ensuring good slidability of the webbing (see, for example, Japanese Utility Model Application Laid-Open (JP-U) No. 1993-44719).
However, in the through anchor disclosed in JP-U No. 1993-44719, the grooves in the surface of the resin piece are formed in a direction which is inclined toward the front of the vehicle with respect to the direction orthogonal to the width direction of the webbing (i.e., the grooves are formed in a direction orthogonal to the width direction of the webbing at the time when the webbing is in its state of usual application to the body of the vehicle occupant). Accordingly, there are cases in which the webbing slips laterally toward the front of the vehicle within the insert-through hole due to the component of force, which is directed toward the front of the vehicle, of the force applied from the grooves to the webbing, and jamming cannot be reliably suppressed.